In an electric power tool of the type including a speed reduction mechanism, use is made of a structure for changing the reduction ratio of the speed reduction mechanism. In this structure, a changeover member such as a ring gear included in a planetary gear mechanism is axially slid to change the engagement state of the planetary gear mechanism.
For example, Japanese Patent Application Publication Nos. 2009-56590 and 2009-78349 disclose electric power tools in which the slide movement of a changeover member including a ring gear is automatically carried out by a solenoid. In such conventional electric power tools, when the solenoid is operated, the rotation of a motor is stopped or reduced in order to suppress a shock occurring when a changeover member is engaged with a counterpart gear member.
In the conventional electric power tool, when the current of the motor or the like is changed, the solenoid is started up and the rotation of the motor is stopped at a preset timing by a control unit that has detected such change.
However, there is somewhat of a difference between a timing at which the solenoid is started up and the changeover member is actually engaged with the counterpart gear member through a plurality of mechanisms and a timing at which the rotation of the motor is reduced and actually stopped.
For that reason, in the conventional electric power tool mentioned above, there has been employed a method for suppressing the engagement shock to the minimum by reliably performing the stopping of the motor or the like before driving the solenoid. However, it is difficult to complete the change of the reduction ratio in a short time by using the method.
In other words, the conventional electric power tool is not sufficient both to suppress the engagement shock when the reduction ratio is changed and to complete the change of the reduction ratio smoothly in a short time.